Distinguish between excess server load and excessive connection work.

src/cpp/ripple/RPCErr.cpp

@@ -72,6 +72,7 @@ Json::Value rpcError(int iError, Json::Value jvResult)
 		{ rpcUNKNOWN_COMMAND,		"unknownCmd",		"Unknown method."										},
 		{ rpcWRONG_SEED,			"wrongSeed",		"The regular key does not point as the master key."		},
 		{ rpcTOO_BUSY,				"tooBusy",			"The server is too busy to help you now."               },
+		{ rpcSLOW_DOWN,				"slowDown",			"You are placing too much load on the server."			},
 	};
 
 	int		i;